Hydride Lattice Research Articles

Orthogonal chemistry in the design of rare-earth metal oxyhydrides

Abstract Inorganic systems containing two or more kinds of anions, such as rare-earth metal oxyhydrides, have a number of interesting properties that can be used in the design and development of new functional materials with desired characteristics. Chemical synthesis of these materials can be accomplished by oxidation of metal hydrides. However, the oxidation process of a metal hydride is directly accompanied by the release of hydrogen; both processes are a combination of two sequential reactions. This is usually not favorable for the formation and crystallization of the ternary oxyhydride composition. One possible way to overcome this problem is to introduce an appropriate amount of oxygen atoms into certain interstitial positions adjacent to the metal sites of the hydride lattice. Guided by the ideas of orthogonality, we have proposed a theoretical model capable of providing a thorough understanding of the chemical processes occurring in a multicomponent system at the molecular level. This model opens the way for predicting a wide range of new, stable multi-anion compounds of different compositions. It can also control functionality by adding noncovalent interactions between different kinds of anions, which can lead to the formation of chiral structures or a significant increase in ferro- and piezoelectric properties.

Interstitial hydrogen atoms in face-centered cubic iron in the Earth\u2019s core

Hydrogen is likely one of the light elements in the Earth’s core. Despite its importance, no direct observation has been made of hydrogen in an iron lattice at high pressure. We made the first direct determination of site occupancy and volume of interstitial hydrogen in a face-centered cubic (fcc) iron lattice up to 12 GPa and 1200 K using the in situ neutron diffraction method. The transition temperatures from the body-centered cubic and the double-hexagonal close-packed phases to the fcc phase were higher than reported previously. At pressures <5 GPa, the hydrogen content in the fcc iron hydride lattice (x) was small at x < 0.3, but increased to x > 0.8 with increasing pressure. Hydrogen atoms occupy both octahedral (O) and tetrahedral (T) sites; typically 0.870(±0.047) in O-sites and 0.057(±0.035) in T-sites at 12 GPa and 1200 K. The fcc lattice expanded approximately linearly at a rate of 2.22(±0.36) Å3 per hydrogen atom, which is higher than previously estimated (1.9 Å3/H). The lattice expansion by hydrogen dissolution was negligibly dependent on pressure. The large lattice expansion by interstitial hydrogen reduced the estimated hydrogen content in the Earth’s core that accounted for the density deficit of the core. The revised analyses indicate that whole core may contain hydrogen of 80(±31) times of the ocean mass with 79(±30) and 0.8(±0.3) ocean mass for the outer and inner cores, respectively.

Study of phase stability and isotope effect in dysprosium trihydride at high pressure

Synchrotron X-ray and Raman scattering investigations have been performed on dysprosium trihydride at high pressure up to 40 GPa. Structural phase transformation from original hexagonal to cubic phase has been observed confirming predictions from other studies and theoretical calculations. Dysprosium trihydride is the last one that has not been studied so far among the heavier lanthanide trihydrides family. These studies completed the overall picture of hexagonal to cubic phase transition for the whole ReH3 compounds. Equation of state and Gruneisen mode parameters have been calculated. High pressure Raman scattering performed on dysprosium deuteride unveiled significant deviation from the harmonic approximation in specific modes most probably due to the anharmonicity of hydrogen potential in the hydride lattice.

Clean Hydrogen Generation through Mechanism of Hydrogen Embrittlement in Metal Hydride Lattice and Exothermal Reaction of Lenr Low Energy Nuclear Reaction

Clean Hydrogen Generation through Mechanism of Hydrogen Embrittlement in Metal Hydride Lattice and Exothermal Reaction of Lenr Low Energy Nuclear Reaction

First-Principles Study on Hydrogen Desorption Properties of Li&lt;sub&gt;4&lt;/sub&gt;BN&lt;sub&gt;3&lt;/sub&gt;H&lt;sub&gt;10&lt;/sub&gt; Doped by Chlorine Anion

The hydrogen storage properties of Li4BN3H10doped by Cl anion are investigated by using first-principles method based on density functional theory. According to the calculated results of formation enthalpy and substitution enthalpy, Cl-doping may result in the substitution of H by Cl-in the hydride lattice and accordingly, a favorable thermodynamics modification. The electronic structure analysis indicates that the main peak of H-1s moves close to Fermi level when substituting H-by Cl-. The stability of hydrogen in the doped hydride is lowered compared with that in the hydride without doping, which improves the hydrogen desorption properties of the hydride.

A prospect for LiBH4 as on-board hydrogen storage

Abstract In contrast to the traditional metal hydrides, in which hydrogen storage involves the reversible hydrogen entering/exiting of the host hydride lattice, LiBH4 releases hydrogen via decomposition that produces segregated LiH and amorphous B phases. This is obviously the reason why lithium borohydride applications in fuel cells so far meet only one requirement — high hydrogen storage capacity. Nevertheless, its thermodynamics and kinetics studies are very active today and efficient ways to meet fuel cell requirements might be done through lowering the temperature for hydrogenation/dehydrogenation and suitable catalyst. Some improvements are expected to enable LiBH4 to be used in on-board hydrogen storage.

Double-locked nucleation and growth kinetics in Nb-H thin films

The kinetics of hydride precipitation in epitaxial Nb films are studied by means of scanning tunneling microscopy (STM) using hydrogen gas loading. Due to the clamped state of thin films, hydride formation results in strong unidirectional out-of-plane film expansion that can be easily detected with STM. Hydrides are found to initially form with cylindrical morphology, leading to typical surface topographies. Their localized expansion allows the analysis of the hydride lattice matching, which is coherent (H1) at the initial stages and semicoherent (H2) at later stages. The volume fraction of H1 and H2 precipitates changes with time. At initial stages, the coherent precipitates dominate, while at later stages semicoherent precipitates become the dominant ones. The relative occurrence of H1 and H2 is bimodal. A maximum occurrence of 30--40 nm sized H1 hydrides is found, which is related to coherency stress between the hydride and the Nb matrix hindering a further hydride growth. It is further demonstrated that for Nb-H films adhered to substrates, the system can be locked in the two-phase region of the phase diagram (here at 10${}^{\ensuremath{-}4}$ Pa at about 50% of hydride). This is different from bulk Nb-H, where the complete sample transforms into a hydride when the hydride formation equilibrium pressure is exceeded. Impact parameters on the lateral hydride arrangement are studied. The impact of the Pd-island surface coating and the intrinsic dislocation network on the precipitation density and arrangement appear to be negligible. However, the substrate miscut and, thus, the surface roughness exhibit a strong influence on hydride nucleation. The H1 hydride arrangement along (111) and the directed H2 hydride growth along (111) are governed by the elastically soft matrix lattice orientations.

Heat capacity measurement and DSC study of hafnium hydrides

Heat capacities, electrical conductivities and phase transition temperature of hafnium hydrides, HfHx (0.99≤x≤1.83), were studied using a direct heating pulse calorimeter and a differential scanning calorimeter from room temperature to above 500 K. The heat capacity of HfH1.83 was larger than that of pure hafnium and showed no anomaly of heat capacity. In contrast, there were λ-type peaks for the heat capacity and DSC curves for HfHx (1.1≤x≤1.6) near 385 and 356 K. The anomalies of heat capacity and electrical conductivity of HfHx (1.1≤x≤1.6) were considered the result of phase transition and order-disorder phase transition for hydrogen in the hafnium hydride lattice for HfHx (1.1≤x≤1.3).

Functional anion concept: effect of fluorine anion on hydrogen storage of sodium alanate

Doping NaAlH(4) with Ti-catalyst has produced a promising hydrogen storage system that can be reversibly operated at moderate temperature conditions. Of the various dopant precursors, TiCl(3) was well recognized due to its pronounced catalytic effect on the reversible dehydrogenation processes of sodium aluminium hydrides. Quite recently we experimentally found that TiF(3) was even better than TiCl(3) in terms of the critical hydrogen storage properties of the doped hydrides, in particular the dehydriding performance at Na(3)AlH(6)/NaH + Al step at moderate temperature. We present here the DFT calculation results of the TiF(3) or TiCl(3) doped Na(3)AlH(6). Our computational studies have demonstrated that F(-) and Cl(-) anions differ substantially from each other with regard to the state and function in the doped sodium aluminium hydride. In great contrast to the case of chloride doping where Cl(-) anion constitutes the "dead weight" NaCl, the fluoride doping results in a substitution of H(-) by F(-) anion in the hydride lattice and accordingly, a favorable thermodynamics adjustment. These results well explain the observed dehydriding performance associated with TiF(3)/TiCl(3)-doping. More significantly, the coupled computational and experimental efforts allow us to put forward a "functional anion" concept. This renews the current mechanism understanding in the catalytically enhanced sodium alanate.

Advantage of TiF 3 over TiCl 3 as a dopant precursor to improve the thermodynamic property of Na 3AlH 6

The effect of the dopant anion on thermodynamic tailoring in TiF(3)- and TiCl(3)-doped Na(3)AlH(6) was investigated by pressure-composition desorption isotherm measurements. It was found that the dissociation pressure of the TiF(3)-doped hydride was substantially higher than that of the TiCl(3)-doped sample. This finding agrees well with the theoretically demonstrated thermodynamic modification arising upon F(-) substitution in the hydride lattice, thus providing direct experimental evidence to support functionality of F(-) anion. (c) 2006 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Hydrogen self-dynamics in orthorhombic alkaline earth hydrides through incoherent inelastic neutron scattering

Inelastic neutron scattering patterns from polycrystalline CaH 2, SrH 2 and BaH 2, measured on TOSCA-II spectrometer at low temperature in the energy transfer range 3 meV < E < 500 meV are reported. From the medium-energy regions, coinciding with optical phonon bands, high-quality generalized self-inelastic structure factors are extracted and compared to new ab initio lattice dynamics simulations, accurately reproducing the hydride lattice structures. The overall agreement is found satisfactory, even though not perfect, especially in the first optical phonon zone of BaH 2. In addition, the simulations provide a compelling support to a recent physical interpretation of the recorded spectral features and allowed to separate the contributions produced by the two non-equivalent hydrogen atoms.

Isotope effect in a Cu–H(D) system with hexagonal hydride phase

The decomposition pressure p dec of copper deuteride has been experimentally determined in a diamond anvil cell. The value of 6.8 ± 0.6 GPa is lower than the corresponding pressure of copper hydride. The difference between standard Gibbs energies of decomposition of copper hydride and deuteride has been calculated as equal to − 5.2 kJ mol −1 (H 2). The zero-point energy of hydrogen vibration in the hydride lattice has been obtained applying the localized harmonic oscillator model.

Generating Low-Temperature Layers with Infrared Heating

Cryogenic targets for the National Ignition Facility require uniform solid layers inside spherical capsules at temperatures ~1.5 K below the triple point of hydrogen. Uniform layers have been successfully formed near the triple point. However, upon subsequent cooling the layers degrade. We report here recent attempts to form uniform deuterium hydride (HD) layers 1.5 K below the triple point using infrared (IR) radiation. Pumping the IR collisionally induced vibration-rotation band of solid HD contained inside a transparent plastic shell generates a volumetric heat source in the HD lattice. This in turn allows the formation of a spherical crystalline shell of HD inside the transparent plastic shell. HD layers ~50 μm thick have been formed near the triple point and slowly cooled 1.5 K under high IR power without layer degradation.

Structure of nanocomposite metal hydrides

It has recently been shown that MgH 2–(V, Nb) nanocomposite has very fast hydrogen sorption kinetics. This could be explained by the presence of vanadium which eases hydrogen penetration into the material and by the particular microstructure of this nanocomposite. In order to have a better understanding of the nature and hydrogen desorption mechanism, a systematic structural study has been undertaken. The powder morphology and chemical phase distribution were observed by SEM. X-ray diffraction under hydrogen pressure was performed at different temperatures in order to see the effect of absorption/desorption process on the crystal structure. Crystallite size was evaluated by X-ray powder diffraction peak broadening. Real time X-ray investigations of hydrogen desorption in MgH 2–Nb nanocomposite were performed using synchrotron radiation. For the first time, we were able to get direct evidence of the dehydrogenation mechanism. A metastable new niobium hydride phase associated with the desorption process was detected. This metastable hydride is probably the result of long-range ordering of hydrogen in the niobium hydride lattice in order to facilitate the hydrogen flow.

NMR study of sodium-hydrogen-graphite ternary intercalation compound

Structural and electronic properties have been analyzed for stage-4 sodium-hydrogen-graphite intercalation compound (NaHGIC) using 13 C and 1 H NMR. 13 C NMR revealed the existence of charge transfer from the intercalates to graphite. The layer-by-layer charge distribution was estimated to be − 0.029 e per carbon atom for the bounding layers and − 0.005 e for the interior layers. The 1 H NMR spectrum is consistent with the model of intercalate structure where the planar hydride lattice is placed between the sodium cationic layers. The layer structure and the in-plane concentration of hydride ions are similar to those of potassium-hydrogen (KH)GIC. However, the cation concentration is smaller than that in KHGIC, and a more neutralized intercalate lattice thus formed explains the relatively localized electronic property of NaHGIC. 1 H NMR also shows the existence of a motionally narrowed spectral component of 10–15% in relative intensity at room temperature, attributable to molecular hydrogen rapidly rotating in the voids in the intercalate lattice.

The effect of hyperstoichiometric iron on the hydrogen storage properties of ZrMnFe ternary

The hyperstoichiometric ZrMnFe x system with x = 1.2–1.4 has been studied as a hydrogen storage material. The stoichiometric excess iron exhibits a profound promoting effect on the decomposition pressure of the hydride. The hydrogen capacity was observed to be very sensitive to the hyperstoichiometric iron content. The host metal underwent a 13% lattice expansion with no structural transformation during hydrogenation. The configurational entropy of hydrogen in the hydride phase is similar to that of deuterium in the ZrMn 2 deuteride, suggesting a similar site occupancy situation. The extreme rapidity of hydrogen sorption is attributed to a 3-dimensional network for hydrogen diffusion existing in the hydride lattice.

XPS studies of the surface composition and chemical states of the components of ZrCr2 and ZrCr2H3.6. Surface composition and chemical state of chromium

According to XPS studies, the ZrCr2 and ZrCr2H3.6 surface have been established to contain Cr2O3, Cr(O), Zr2O and nonstoichiometric ZrO2−x. The Cr(O) content increases after thermal vacuum treatment of the samples, particularly after Ar+ sputtering. Active hydrogen evolving from the hydride lattice also promotes the increase in the Cr(O) content. After oxidation, chromium is detected only as Cr2O3.

Structures and stabilities of the group IIIa dihydrides

The CaF 2-type dihydrides of the group IIIa elements represent a relatively large family of similar metallic hydrides for which relationships between interatomic distances and stabilities can be derived. Available data for the thermodynamic properties of formation of these dihydrides were assembled and the enthalpies and free energies of formation are compared with the metal-hydrogen distances in the hydrides. The data show that for these hydrides there is a maximum in the stability-distance curve; the most stable dihydrides are HoH 2 and DyH 2 with metal-hydrogen distances of 2.237Å and 2.252 Å respectively. A modified Born-Mayer ionic model is applied to this family of dihydrides. In addition to the usual Coulomb (attraction) and overlap (repulsion) terms, an additional attraction term is introduced to take into account residual metallic cohesion in the hydride lattice. The results obtained from this model are compared with the thermochemical data using the BornHaber cycle. In making this comparison a parameter β (which has units of length) is introduced which accounts for the influence of the 4f electronic structure on the repulsive potential for the lanthanide dihydrides. It is shown that the relation between stability and the sum of the metallic radius and the tetrahedral hole radius (in the metal) is similar to that between stability and the actual metal-hydrogen distance in these dihydrides. This similarity is used to rationalize observed correlations between stability and tetrahedral hole sizes in intermetallic compound hydrides.

Some applications to materials analysis using deuteron and proton beams of 0.5 to 2.5 MeV

The applications of a conventional 2.5 MeV Van de Graaff machine for analytical work using a beam of accelerated protons or deuterons is described. These applications include (1) the depth concentration of deuterium in steels using a nuclear reaction technique, (2) the location of3He atoms in the erbium hydride lattice using ion channelling and (3) the identification of vanadium oxides formed by sputtering using Rutherford backscattering and electron diffraction. Provisional results are presented.

Neutron Thermalization in Zirconium Hydride

A series of infinite-medium spectral measurements has been performed on ZrH1.75 at room temperature, 150 C, 170 C, 316 C, and 468 C, using the General Atomic linear accelerator as a pulsed-neutron source. Two poison concentrations were used, 3.4 and 8 barns per hydrogen atom. These measurements clearly demonstrated that neutron spectra in zirconium hydride shift rather markedly with temperature. The above spectra were calculated theoretically assuming the hydrogen atoms to be bound in an isotropic harmonic potential, and allowing for the possibility of accoustical vibrations in the zirconium hydride lattice. The agreement between theory and experiment is very good.